CANBERRA, Australia - Former prime minister Kevin Rudd on Tuesday said that Australian authorities must continue to monitor the return of Islamic State foreign fighters after police foiled a terror plot to bring down an Australian plane earlier this week.

The plot, which would have involved either taking a bomb or a deadly gas on board a flight - possibly one from Jakarta to Sydney - was foiled by police on Sunday and resulted in the arrest of at least four people in Sydney.

Speaking to Sky News on Tuesday, Rudd said while authorities would be monitoring channels between the Middle East and Australia for returning foreign fighters, a lot of emphasis must be placed on monitoring those who attempt to return to Australia via Southeast Asia.

"In Australia, what we need to look at so carefully right now, is what is happening in terms of the return of foreign fighters to South East Asia and into Indonesia, in particular," Rudd said.

"That is the thing which concerns me the most. Obviously, in terms of what has happened in Australia and in terms of the alleged bombing effort against an Australian aircraft, I haven't been briefed, but this may be part of the broader reaction to IS being squeezed out of the Middle East."

Meanwhile, Abu Dhabi's Etihad Airways said on Tuesday it was helping Australian police with an investigation that police began into the "Islamic-inspired" plot.

Police have not identified the airline that was allegedly targeted in the plot, nor the specific means that were to be used to bring it down, other than to say it involved an "improvised device".

US officials, on condition of anonymity, said a foreign intelligence service had intercepted communications between the plotters in Sydney and members of the IS group in Syria. The officials declined to identify the foreign intelligence service.

Another two US officials, familiar with the arrests, said a developing plot had been detected. One of them said the plot was "fairly well along" when it was disrupted by Australian authorities.

Xinhua - Reuters